Revert "infra/config Use Goma's task service account."

This reverts commit d6407546.

Reason for revert: broke all builders at gclient runhook

Original change's description:
> infra/config Use Goma's task service account.
> 
> For ease of distinguishing Goma's builder, let me specify special
> service accounts for them.
> 
> Bug: b/166712857
> Change-Id: I45317d787e2b3f8bbf9e1cb15d588ba661fad4fe
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2384450
> Commit-Queue: Yoshisato Yanagisawa <yyanagisawa@chromium.org>
> Commit-Queue: Takuto Ikuta <tikuta@chromium.org>
> Auto-Submit: Yoshisato Yanagisawa <yyanagisawa@chromium.org>
> Reviewed-by: Takuto Ikuta <tikuta@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#802998}

TBR=ukai@google.com,yyanagisawa@chromium.org,tikuta@chromium.org,yekuang@google.com

Change-Id: I5e9bf7044ca1e9a23455e89e99533a42cb18883c
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: b/166712857
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2384573Reviewed-by: Yoshisato Yanagisawa <yyanagisawa@chromium.org>
Commit-Queue: Yoshisato Yanagisawa <yyanagisawa@chromium.org>
Cr-Commit-Position: refs/heads/master@{#803020}

infra/config/generated/realms.cfg

@@ -109,7 +109,7 @@ realms {
   name: "goma"
   bindings {
     role: "role/buildbucket.builderServiceAccount"
-    principals: "user:goma-release-testing@chops-service-accounts.iam.gserviceaccount.com"
+    principals: "user:chromium-ci-builder@chops-service-accounts.iam.gserviceaccount.com"
   }
   bindings {
     role: "role/buildbucket.owner"

infra/config/subprojects/goma/goma.star

@@ -32,7 +32,7 @@ defaults.execution_timeout.set(3 * time.hour)
 defaults.os.set(os.LINUX_DEFAULT)
 defaults.pool.set("luci.chromium.ci")
 defaults.service_account.set(
-    "goma-release-testing@chops-service-accounts.iam.gserviceaccount.com",
+    "chromium-ci-builder@chops-service-accounts.iam.gserviceaccount.com",
 )
 defaults.swarming_tags.set(["vpython:native-python-wrapper"])
 defaults.triggered_by.set(["master-gitiles-trigger"])